Endoscopes are often used in minimally invasive surgical and/or therapeutic procedures, such as laparoscopy, hysteroscopy, and colonoscopy, for example. Near-infrared (NIR) imaging using endoscopes has been described in the literature for various clinical applications. Often, such an imaging modality utilizes a contrast agent (such as indocyanine green, for example) that absorbs and/or fluoresces in the 700-900 nm range of the NIR. Although the preponderance of optical instruments currently in use are not optimized for both visible (VIS) and NIR light imaging, such instruments may still transmit sufficient NIR light that it may also be desirable to enable the previously described VIS-NIR imaging system for use with these conventional optical instruments. Conventional optical instruments are typically well-corrected for imaging throughout the visible spectrum, but without equivalent correction in the NIR, NIR images acquired with the aforementioned VIS-NIR imaging system through such optical instruments are likely to be of poor quality. Furthermore, although some of the NIR image aberrations introduced by conventional optical instruments may be corrected by applying compensating lens design techniques to the optical couplers, such techniques are typically not powerful enough to correct both the aberrations and the shift in focal plane between the visible and NIR images produced with such instruments.
Related art attempted to address some of the deficiencies by devising endoscope optics in which the imaging quality throughout the visible and NIR portions of the spectrum were balanced. This included examples of objective lenses (US 2008/0252997, US 2011/0002051, US 2013/0057666) and a compensated optical coupler device (US 2011/0249323), to name just a few. While addressing some of existing deficiencies of the endoscope optics, these and other examples resemble each other in that they have substantially low apertures (typically corresponding to F/5 to F/11), which does not provide practically-sufficient diffraction-limited resolution for a wide-spectral-range imaging with sensor pixels dimensioned to about 1.5. microns. In addition, the existing solutions do not effectuate optical correction of monochromatic and chromatic aberrations, as well as barrel distortion, to a level that is below practically-acceptable low level(s).
At the same time, the lens designs provided by the related art (which includes the solution disclosed in the U.S. application Ser. No. 15/393,705) are approximately telecentric at the optical sensor (in the image space) and are configured specifically either for use in endoscopes or laparoscopes that do not include what's known in the art as a “microfly's eye array”, or for use with a follow-up telecentric relay lens system (in the case when the optical sensor is proximal to the user/clinician). However, this inevitably translates to the operational requirement that the objective lens be of greater dimension (diameter) than the dimension of the optical sensor (or that the objective lens be bigger than the size of the first image plane). For an endoscope or laparoscope, larger lens diameter is a major disadvantage, as they frustrate the patient and provide no comfort during the procedure. In addition, in a lens system with the telecentric optical design it is more difficult to correct distortion, since there must be negative optical power present in a portion of the lens system preceding the aperture stop and positive optical power in the remaining portion of the lens. Most prior art does not even attempt to correct this distortion. While the U.S. patent application Ser. No. 15/393,705 provides for correction of distortion, it does so with a relatively large, complex design having with multiple aspheric surfaces.
Embodiments of the present invention address these problems.